This invention relates to the deinking of waste printed paper which may be used to make newsprint, magazine or book stock.
Processes for deinking cellulosic materials have been described in U.S. Pat. Nos. 3,392,083 and 3,932,206. Typically, a process includes dispersing, in a large agitated reactor (pulper), cellulosic material, i.e. waste paper, in water containing a non-ionic surfactant and other chemical adjuncts. The resulting dispersion or pulp slurry is washed and diluted with additional water which is introduced using counter current water flow to separate ink from the slurry. The pulp is drained and then used to form paper. It is common to add other constituents during the steps of pulping, washing or just prior to paper formation. These constituents may include chemicals for pH adjustment, inorganic phosphates and dispersing agents, talc to reduce the redeposition of materials previously separated from the pulp, defoaming agents, dyes, bleaching agents, flocculating agents, and sizing agents which impart water resistance to the final paper. Other materials may be used to satisfy specific processing or paper property needs.
Non-ionic surfactants, which typically contain a polyglycol (ethylene oxide) portion, are conventionally used when washing processes are utilized to deink printed paper. They not only aid in the removal of inks by emulsifying and dispersing the ink material, but additionally they may enhance dispersion of the fiber in the water. However, some residual amounts of nonionic surfactant remain in the finished, reconstituted paper, which results in the rapid rewetting of the paper and a reduction of paper strength. When sizing chemicals are used, the residual nonionic surfactant negates the desired water resistance (sizing).
In particular, the residual surfactant is undesirable when the reconstituted paper is used for printing, i.e. off-set printing, where it is desirable to have enhanced water resistance so that the paper is not instantly wetted. Such water resistance reduces the amount of paper web breaks which occur on the printing presses and may impart improved print appearance.
To overcome the deleterious effects of the residual non-ionic surfactant, increasingly larger quantities of sizing chemicals have been used. This has not only proven undesirable economically, but additionally has resulted in finished paper having less favorable brightness, strength and other physical properties, as well as paper machine processing difficulties. Moreover, introduction of a greater amount of sizing agent has not always been effective in imparting the desired water resistance and is additionally deleterious to strength.